The present application is concerned with information signal coding using different coding modes differing, for example, in effective coded bandwidth and/or energy preserving property.
In [1], [2] and [3] it is proposed to deal with short restrictions of bandwidth by extrapolating the missing content with a blind BWE in a predictive manner. However, this approach does not cover cases, in which the bandwidth changes on a long-term basis. Also, there is no consideration of different energy preserving properties (e.g. blind BWEs usually have significant energy attenuations at high frequencies compared to a full-band core). Codecs using modes of varying bandwidth are described in [4] and [5].
In mobile communication applications, variations of the available data rate that also affect the bitrate of the used codec might not be unusual. Hence, it would be favorable to be able to switch the codec between different, bitrate dependent settings and/or enhancements. When switching between different BWEs and e.g. a full-band core is intended, discontinuities might occur due to different effective output bandwidths or varying energy preserving properties. More precisely, different BWEs or BWE settings might be used dependent on operating point and bitrate (see FIG. 1): Typically, for very low bitrates a blind bandwidth extension scheme is of advantage, to focus the available bitrate at the more important core-coder. The blind bandwidth extension typically synthesizes a small extra bandwidth on top of the core-coder without any additional side-information. To avoid the introduction of artifacts (e.g. by energy overshoots or amplification of misplaced components) by the blind BWE, the extra bandwidth is usually very limited in energy. For medium bitrates, it is in general advisable to replace the blind BWE by a guided BWE approach. This guided approach uses parametric side-information for energy and shape of the synthesized extra bandwidth. By this approach and compared to the blind BWE, a wider bandwidth at higher energy can be synthesized. For high bitrates, it is advisable to code the complete bandwidth in the core-coder domain, i.e. without bandwidth extension. This typically provides a near perfect preservation of bandwidth and energy.
Accordingly, it is an object of the present invention to provide a concept for improving the quality of codecs supporting switching between different coding modes, especially at the transitions between the different coding modes.